Anti-insulin antiserum increases inositol phosphate accumulation in rat pancreatic islets

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Abstract
The role of insulin in modulating phosphoinositide breakdown and accumulation of inositol phosphates was investigated in isolated rat pancreatic islets by using GPAIS (guinea-pig anti-insulin antiserum) that neutralizes effects of insulin in the medium. At either 3.0 mM- or 16.7 mM-glucose or 3.0 mM-glucose plus 10 .mu.m-arecaidine propargyl ester (muscarinic receptor agonist), GPAIS (but not control serum) was able to increase InsP2 and InsP3, but not InsP, in myo[3H] inositol-prelabelled islets. The effect on GPAIS on 3H incorporation into InsP3 was dose-dependent, with a half-maximal effect at a concentration able to bind 4004 .+-. 163 .mu.units of insulin. A specific mass assay of the biologically relevant isomer Ins (1,4,5)P3 revealed a high increase (> 3-fold). Formation of PtdIns, PtdInsP and PtdInsP2 was not affected by GPAIS. This is indirect evidence for an effect of insulin on inositide metabolism, and therefore endogenously released insulin may have led to an underestimation in earlier studies of effects of insulinotropic substances on inositol phosphate accumulation.